Digital alloys and methods for forming the same

ABSTRACT

Alloys of tunable compositions and corresponding optical, electrical and mechanical properties are described. Also described are their uses in optoelectronic devices and material interfaces.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/158,596, filed May 30, 2002; which claims the benefit under35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/325,664filed on Sep. 28, 2001.

This application is also a continuation-in-part of U.S. patentapplication Ser. No. 10/965,227, filed Oct. 15, 2004; which claims thebenefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent ApplicationNo. 60/511,102 filed Oct. 15, 2003.

This application is also a continuation-in-part of U.S. patentapplication Ser. No. 11/254,540, filed Oct. 19, 2005, which claims thebenefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent ApplicationNo. 60/620,522 filed Oct. 19, 2004.

This application also claims the benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Patent Application No. 60/801,792, filed May 19, 2006,where these applications are incorporated herein by reference in theirentireties.

BACKGROUND

1. Technical Field

This application is related to alloys with controllable compositions andphysical properties, including optoelectrical and mechanical properties,their use in optoelectronic devices and methods of making such alloys.

2. Description of the Related Art

Optoelectronic devices include a wide range of electrical-to-optical, oroptical-to-electrical transducers, such as photodiodes (including solarcells), phototransistors, light-dependent resistors, lasers,light-emitting diodes (LED), fiber optics and the like. Regardless ofthe type, an optoelectronic device operates based on at least one of twofundamental processes, namely, creating electron-hole pairs by photonabsorption, or emitting photons by recombining electrons and holes.

Semiconductor materials have unique electronic band structures, whichcan be impacted by the quantum mechanical effect of light. They are thusmaterials of choice in fabricating optoelectronic devices. In asemiconductor material, the uppermost-occupied band is typicallycompletely filled and is referred to as a valence band; whereas thelowest unoccupied band is referred to as a conduction band. Electrons inthe valence band can absorb photon energy and be excited to theconduction band, leaving holes in the valence band. The semiconductormaterial becomes conductive when an appreciable number of electrons arepresent in the conduction band. Conversely, electrons in the conductionband can be recombined with a hole in the valence band and causespontaneous or stimulated emission of photons.

The optical and electrical properties of a semiconductor material arelargely determined by the energy difference (“band gap”) between itsvalence band and conduction band. For example, during the process ofcreating electron-hole pairs, the bandgap is a direct measure of theminimum photon energy required to excite an electron from the valenceband to the conduction band. When an electron and hole recombine, thebandgap determines the photon energy emitted. Accordingly, controllingthe bandgap is an effective way of controlling the optical andelectrical properties and outputs of the optoelectronic devices.

The bandgap is an intrinsic property of a given semiconductor material.Bandgaps can be adjusted by doping a semiconductor material with animpurity according to known methods. Alternatively, semiconductor alloysformed by two or more semiconductor components have been created. Thebandgap of such an alloy is different from that of the semiconductorcomponents, and is typically a function of the bandgaps and the relativeamounts of the components.

Generally speaking, in creating a new alloy, two or more elements areallowed to grow into one crystal lattice. More commonly, two types ofbinary alloys (e.g., AlAs, InP, GaAs and the like) are grown into atertiary or quaternary alloy. Lattice match of the components istherefore important in reducing the strain and defects of the resultingalloy.

FIG. 1 shows the bandgap energies (eV) and lattice constants of variousGroup III-V semiconductors. As illustrated, two binary semiconductoralloys, AlAs and GaAs, have nearly identical lattice constants (about5.65). Their bandgaps are respectively 2.20 eV and 1.42 eV. Because ofthe matching lattice constants, AlAs and GaAs are suitable to form arelatively stable tertiary alloy, which can be represented byAl_(x)Ga_(1-x)As (x being the atomic percentage of AlAs in the alloy).The bandgap of the tertiary alloy is a function of x as well as thebandgaps of the pure AlAs and GaAs. This example illustrates an approachto engineering bandgaps by controlling the compositions of semiconductoralloys.

Controlling the composition of an alloy shows promise for creating newmaterials with tunable optoelectrical or mechanical properties.Currently, semiconductor alloys such as Al_(x)Ga_(1-x)As,In_(x)Ga_(1-x)N and Al_(x)Ga_(1-x)N are fabricated by epitaxial growthtechniques such as Metal Organic Chemical Vapor Deposition (MOCVD) orMolecular Beam Epitaxy (MBE). However, technical challenges remain ingrowing these epitaxial layers, in spite of the relativestrain-tolerance and defect-tolerance of the materials. In particular,their mechanical stability and integrity are difficult to maintain dueto strain, which, in turn, limits the thickness of the layers grown. Thecompositional control is also influenced by the strain in the material.

Some semiconductor materials do not have an acceptable lattice matchthat will permit them to be formed in a stable compound orheterostructure using standard bulk crystal or epitaxial growthtechniques. Thus, engineering a specific bandgap or having a particularalloy composition is very difficult and sometimes not possible withcurrent semiconductor technology

BRIEF SUMMARY

Semiconductor or metal alloys based on templated formation of elementaland/or binary nanostructure components (or “nanocomponents” aredescribed. Generally speaking, templates are provided or engineered tocomprise a plurality of different types of binding sites at controllableratios, and with nanometer-scale site-to-site distances. A first type ofbinding sites is selected which have specific affinities for a firsttype of nanostructure components, whereas a second type of binding sitesis selected which have specific affinities for a second type ofnanostructure components. The first and second types of nanostructurecomponents are bound to the templates in a controllable manner. Thetemplates can be assembled and cause the first and second type ofnanostructure components to form a new material that emulates amulti-element alloy. The nanostructure components, the size of thenanocomponents and their placement on the template, together with theratio, can be selected so that the collection of the discretenanocomponents emulates a multi-element alloy.

In addition, methods of making the alloys and devices that employ suchalloys are also described.

More specifically, one embodiment provides a composition comprising: aplurality of templates, each template comprising at least one firstbinding site and at least one second binding site, the first bindingsite having a specific binding affinity for a first nanoparticle of afirst material, the second binding site having a specific bindingaffinity for a second nanoparticle of a second material, wherein thetemplates are selected to include, in percentages, x first binding sitesand y second binding sites; a plurality of the first nanoparticles boundto respective first binding sites; a plurality of the secondnanoparticles bound to respective second binding sites; wherein thetemplates are assembled such that the first material and the secondmaterial form an alloy at a stoichiometric ratio of x:y.

A further embodiment provides a method of forming an alloy, the methodcomprising: forming at least one biological template having at least onefirst binding site and at least one second binding site, the firstbinding site having a specific binding affinity for a first nanoparticleof a first material, the second binding site having a specific bindingaffinity for a second nanoparticle of a second material; controlling thetemplate such that the first binding sites and the second binding siteshave a number ratio of x:y (0<x<1, 0<y<1); binding the firstnanoparticles to respective first binding sites; binding the secondnanoparticles to respective second binding sites; and forming the alloycomprising the first material and the second material.

Another embodiment provides an optoelectronic device comprising analloy, the alloy being formed by: forming a plurality of biologicaltemplates, each templates having a first plurality of binding sites anda second plurality of binding sites, the template having a selectedratio of the first binding sites to the second binding sites; coupling aplurality of first nanoparticle components to the first plurality ofbinding sites on the biological template, the first component beingcomposed of at least two different elements; coupling a plurality ofsecond nanoparticle components to the second plurality of binding siteson the template, the second component being composed of at least twodifferent elements, at least one element of the second component beingdifferent from at least one element of the first component; the ratio ofthe number of first binding sites to the second binding sites beingselected so that the templates can assemble the first plurality ofnanoparticles and the second plurality of nanoparticles into the alloy.

A further embodiment provides an optoelectronic device comprising analloy as described above, further provided that the plurality ofbiological templates is removed after the alloy is formed.

Another embodiment provides a solar cell structure, which comprises: asemiconductor substrate; a light sensitive layer coupled to thesemiconductor substrate, the light sensitive layer comprising an alloy,which includes: a plurality of templates, each templates having a firstplurality of binding sites and a second plurality of binding sites, thetemplate having a selected ratio of the first binding sites to thesecond binding sites; a plurality of first nanoparticle componentscoupled to the first plurality of binding sites on the biologicaltemplate, the first component being composed of at least two differentelements; a plurality of second nanoparticle components being coupled tothe second plurality of binding sites on the template, the secondcomponent being composed of at least two different elements, at leastone element of the second component being different from at least oneelement of the first component; the ratio of the number of first bindingsites to the second binding sites being selected so that the templatescan assemble the first plurality of nanoparticles and the secondplurality of nanoparticles into the alloy.

A further embodiment provides a lithium-ion battery comprising: an anodethat includes cobalt, oxygen and a low resistivity metal selected fromthe group consisting essentially of gold, copper and silver, the ratioof the low resistivity metal to the cobalt being selectively controlledto be less than 4 and positioned within the anode to reduce the cellresistance of the battery; a cathode; and an electrolyte fluidpositioned between the anode and the cathode to transfer lithium ions,wherein, the cobalt and low resistivity metals are formed in the presentof a plurality of templates, each template having a plurality of firstbinding sites with an affinity for cobalt and a plurality of secondbinding sites with an affinity for the low resistivity metal, the numberof the binding sites for the low resistivity metal being substantiallyless than the number of the binding sites for the cobalt and having aselected ratio of first and second binding sites.

Another embodiment provides a structure comprising: a first conductivelayer; a second conductive layer; and an intermetallic layer positionedbetween the first conductive layer and the second conductive layer, theintermetallic layer being formed by forming at least one biologicaltemplate having at least one first binding site and at least one secondbinding site, the first binding site having a specific binding affinityfor a first nanoparticle of a first material, the second binding sitehaving a specific binding affinity for a second nanoparticle of a secondmaterial, controlling the template such that the first binding sites andthe second binding sites have a number ratio of x:y (0<x<1, 0<y<1),binding the first nanoparticles to respective first binding sites,binding the second nanoparticles to respective second binding sites; andforming an alloy comprising the first material and the second material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are not intendedto convey any information regarding the actual shape of the particularelements, and have been selected solely for ease of recognition in thedrawings.

FIG. 1 is a well-known bandgap energy and lattice constant graph.

FIGS. 2A and 2B show schematically a digital alloy and the resultingbandgap according to one embodiment.

FIG. 3 shows an engineered bandgap according to one embodiment.

FIGS. 4A and 4B illustrate schematically a template and binding sitesaccording to different embodiments.

FIGS. 5A and 5B illustrate schematically different chaperonins accordingto various embodiments.

FIG. 6 shows schematically an ordered 2D array of templates according toone embodiment.

FIG. 7 illustrates a template for achieving a ternary compound bandgapusing only binary components.

FIG. 8 illustrates a template having engineered binding sites at aselected ratio for specific nanoparticles according to one embodiment.

FIG. 9 illustrates the nanoparticles coupled to the respective bindingsites of the template of FIG. 8.

FIG. 10 illustrates a first ratio of binding sites for binary componentsto emulate a selected ternary compound.

FIG. 11 illustrates a different ratio of the same binding sites toemulate a different ternary compound.

FIGS. 12A and 12B illustrate a solar cell having a plurality of layerswhich emulate ternary compounds made according to principles illustratedin FIGS. 10 and 11.

FIG. 13 illustrates schematically the various bandgaps of materials in asolar cell.

FIG. 14 illustrates schematically, various nanorods on a templateaccording to the invention.

FIG. 15 illustrates schematically the nanorods of FIG. 14 used in anoptoelectronic device.

FIG. 16 illustrates a template having a selected ratio of binding sitesfor elements to emulate a specific compound.

FIG. 17 illustrates a template for the same elements, having a differentratio of binding sites to emulate a different compound.

FIG. 18 illustrates a lithium ion battery having gold elements atselected locations in the anode or cathode according to principles ofthe present invention as illustrated in FIGS. 16 and 17.

FIG. 19 is a schematic diagram of an LED made according to oneembodiment.

FIG. 20 illustrates schematically an intermetallic structure accordingto one embodiment.

DETAILED DESCRIPTION

Alloys with precision-controlled compositions are described. Thesealloys, also referred to herein as “digital alloys,” are hybrids of twoor more types of nanostructure components (e.g., “nanocrystals”), whichare assembled in the presence of templates. As will be described furtherin detail, a nanostructure component is a nanoscale building block andcan be an elemental material (including a single element) or a binary(including two elements) material. The templates are biological ornon-biological scaffolds including binding sites that specifically bindto selected nanocrystals, and where the binding sites are separated bydistances on the order of nanometers or 10's of nanometers. Thecomposition of the digital alloy is determined by the nanocrystalcomponents at a stoichiometry controlled by the distribution of thebinding sites.

Due to the small dimensions of the nanocrystals (typically only a fewatoms) and their proximity to each other (typically a few nanometers totens of nanometers), electrons cannot distinguish one nanocrystalcomponent from another nanocrystal component as discrete materials.Instead, the electron behavior averages over the two or more differentmaterials in the nanocrystals and perceives them as a single alloy.Thus, new materials of tunable macroscopic properties can be created bymanipulating the nanoscale components.

FIG. 2A shows schematically a digital alloy 10 made up of thin layers oftwo types of binary nanocrystals, 20% of a first binary nanocrystal 14(e.g., InN) and 80% of a second nanocrystal 18 (e.g. GaN). FIG. 2Billustrates how an electron 30 perceives the digital alloy 10. From anelectron's point of view, the conduction bands 34 of GaN and theconduction band 38 of InN are averaged to obtain a conduction band 42 ofthe digital alloy, which may be represented by In_(0.2)Ga_(0.8)N.Similarly, the valence bands of GaN 46 and the valence band 50 of InNare averaged out to obtain a valence band 54 of the alloy correspondingto In_(0.2)Ga_(0.8)N. The bandgap energy of the digital alloy is thus avalue between the bandgap energies of the pure InN and GaN. In otherwords, electrons perceive the alloy 10 as a ternary alloy of a newcomposition (In_(0.2)Ga_(0.8)N), not as being two separate binarycomponents InN and GaN. As will be described in detail below, thestoichiometry of each element in the new composition is controlled byusing templates that are designed to bind to the two binary componentsat a selected ratio (e.g., 20%:80% for InN and GaN in FIG. 2A). Thebandgap for this ternary alloy is a function of the stoichiometry of theindividual components.

Macroscopically speaking, the assembled nanocrystal components emulate anew bulk material that has averaged properties of that of the componentmaterials. These digital alloys therefore correspond to a wide range ofoptical, electrical and mechanical properties, which are typicallyunattainable in naturally occurring materials. For example, two layersof indium gallium nitride (InGaN), one tuned to a bandgap of 1.7 eV andthe other to 1.1 eV, could attain the theoretical 50% maximum efficiencyfor a two-layer multi-junction cell. Epitaxial growth of InGaN with ahigh % of In is currently difficult to achieve without materialinhomogeneities and low optical efficiency. Currently, materials withspecifically designed and selected bandgaps are often difficult toconstruct, however according to the methods described herein, suchlayers can be easily constructed having any selected bandgap, if thebinary nanostructures are available.

Thus, certain embodiments are directed to an alloy comprising: aplurality of templates, each template including at least one firstbinding sites and at least one second binding sites, the first bindingsite having a specific binding affinity for a first nanoparticle of afirst material, the second binding site having a specific bindingaffinity for a second nanoparticle of a second material, the templatesare selected to include, in percentages, x first binding sites and ysecond binding sites; a plurality of the first nanocrystals bound torespective first binding sites; a plurality of the second nanocrystalsbound to respective second binding sites; wherein the templates areassembled such that the first material and the second material form analloy of the first material and the second material at a stoichiometricratio of x:y.

FIG. 3 illustrates the engineering of a desired bandgap according to acompositional control of a digital alloy. As used herein, the term“digital alloy” refers to combinations of any materials, includingsemiconductors, metals, metal oxides and insulators. As shown in FIG. 3,a first material (e.g., GaN) has a conduction band 20 and a valence band21. The distance d1 between the conduction band 20 and the valence band21 is the bandgap. For insulators, the bandgap is usually higher than 3eV and cannot be overcome by electrons in the valence band, whereas formetallic conductors, there is no bandgap and the valence band overlapsthe conduction band. In semiconductors, as described above, the bandgapis sufficiently small that electrons in the valence band can overcomethe bandgap and be excited to the conduction band under certainconditions. FIG. 3 also illustrates the bandgap of a second material,(e.g., InN), having a conduction band 22 and a valence band 23, andtherefore having a bandgap represented by the distance d2 between thetwo bands. A template is created having first binding sites and secondbinding sites in a user-designed and selected ratio (x:y), x and y beingthe percentages of the first and second binding sites and x+y is 1. Thefirst and second binding sites are selected to bind to first and secondmaterials, respectively. The ratio of the first material and the secondmaterial on the template is therefore in a stoichiometric ratio of x:y.The resulting digital alloy, as made from the two components (e.g.,In_(x)Ga_(y)N or In_(x)Ga_(1-x)N), will therefore have a valence band25, a conduction band 24, and an engineerable bandgap d based on theidentities and the stoichiometry of the two components.

As used herein, x and y can be represented by proper fractions orpercentages (0<x<1, 0<y<1). For instance, in a two-component alloy(i.e., x+y=1), if the first binding site is present at x=20% of thecombined first binding sites and second binding sites, it is understoodthat x can also be represented as a proper fraction 0.2. Moreover, aselected ratio of the first binding sites and second binding sites canbe represented by x:y, this ratio corresponds to the stoichiometricratio of the two materials made up the resulting alloy.

FIG. 4A illustrates a template 50 comprising a scaffold 54 includingfirst binding sites 58 and second binding sites 62 at a selected ratioof 20%:80%. The first binding sites 58 are coupled to first nanocrystals66 with specificity, and the second binding sites 62 are coupled tosecond nanocrystals 70 with specificity. Thus, if the first nanocrystalsare InN and the second nanocrystals are GaN, the resulting alloy formedby assembling the templates 50 can be represented by In_(0.2)Ga_(0.8)N.

FIG. 4B illustrates another template 80 comprising the scaffold 84including first binding sites 58 and second binding sites 62 at aselected ratio of 40%:60%. As will be discussed in more detail below,the same types of binding sites and the same corresponding nanocrystalsas those illustrated in FIG. 4A can be used. However, the selected ratioof the first binding sites and the second binding sites are tuned to40%:60%. Thus, if the first nanocrystals are InN and the secondnanocrystals are GaN, the resulting alloy formed by assembling thetemplates 80 can be represented by In_(0.4)Ga_(0.6)N.

Thus, alloys can be synthesized in a controllable fashion usingappropriate templates, in particular, by selecting a ratio of bindingsites that correspond to different nanocrystal components. The resultingalloy, which is made up by nanoscale building blocks of two or moredifferent materials, is not constrained by lattice match or geometriesthereof. Physical properties, such as optical, electrical, magnetic andmechanical properties that are innately associated with a givencomposition of alloy, will be averaged over those of the nanocrystalcomponents. Depending on the desired end use, semiconductor alloys andmetallic alloys can be prepared based on semiconductor nanocrystals andmetallic nanocrystals, respectively, as explained later herein.

A. Templates

“Templates” can be any synthetic and natural materials that providebinding sites to which nanocrystals can be coupled. As used herein, thetemplates are selected such that precision control of the binding sites,in terms of their composition, quantity and location can be achieved ina statistically significant manner. Both biological and non-biologicalbased templates can be used.

Because peptides sequences have been demonstrated to have specific andselective binding affinity for many different types of nanocrystals,biological templates incorporating peptide sequences as binding sitesare preferred. Moreover, biological templates can be engineered tocomprise pre-determined binding sites in pre-determined spatialrelationships (e.g., separated by a few to tens of nanometers). They areparticularly advantageous for controlling the compositions of digitalalloys. Biological templates include, for example, biomolecules andbiological scaffold fused with peptide sequences.

As will be described in more detail below, biological templates can bemanipulated through genetic engineering to generate specific bindingsites at controllable locations on the templates. Non-biologicaltemplates can also be manipulated through precision patterning ofbinding sites at nanoscale resolutions.

1. Biological Templates:

As noted above, biological templates such as proteins and biologicalscaffolds can be engineered based on genetics to ensure control over thetype of binding sites (e.g., peptide sequences), their locations on thetemplates and their respective density and/or ratio to other bindingsites. See, e.g., Mao, C. B. et al., (2004) Science, 303, 213-217;Belcher, A. et al., (2002) Science 296, 892-895; Belcher, A. et al.,(2000) Nature 405 (6787) 665-668; Reiss et al., (2004) Nanoletters, 4(6), 1127-1132, Flynn, C. et al., (2003) J. Mater. Sci., 13, 2414-2421;Mao, C. B. et al., (2003) PNAS, 100 (12), 6946-6951, which referencesare hereby incorporated by reference in their entireties.Advantageously, this allows for the ability to control the compositionand distribution of the binding sites on the biological template.

In certain embodiments, the biological template comprises, inpercentages, x first peptide sequences and y second peptide sequences.Because of the specific affinity of the first peptide sequence for afirst nanocrystal of a first material, and the second peptide sequencefor a second nanocrystal of a second material, an alloy of the firstmaterial and the second material can be formed. More specifically, thealloy comprises the first material and the second material in a selectedstoichiometry (x:y) determined by the relative amounts of the firstbinding sites and the second binding sites.

In other embodiments, it is not necessary that both the first bindingsites and the second binding sites are present on a single type oftemplate. Instead, the first binding sites may be present exclusively ona first type of template, and the second binding sites on a second typeof template. The relative percentage of the first binding sites andsecond binding sites (x:y) can be controlled by a selected ratio of thefirst type of template and the second type of templates in the alloycomposition.

a. Biomolecules

In certain embodiments, the biological templates are biomolecules suchas proteins. “Biomolecule” refers to any organic molecule of abiological origin. Typically, a biomolecule comprises a plurality ofsubunits (building blocks) joined together in a sequence via chemicalbonds. Each subunit comprises at least two reactive groups such ashydroxyl, carboxylic and amino groups, which enable the bond formationsthat interconnect the subunits. Examples of the subunits include, butare not limited to: amino acids (both natural and synthetic) andnucleotides. Examples of biomolecules include peptides, proteins(including cytokines, growth factors, etc.), nucleic acids andpolynucleotides. A “peptide sequence” refers to two or more amino acidsjoined by peptide (amide) bonds. The amino-acid building blocks(subunits) include naturally occurring α-amino acids and/or unnaturalamino acids, such as β-amino acids and homoamino acids. Moreover, anunnatural amino acid can be a chemically modified form of a naturalamino acid. “Protein” refers to a natural or engineered macromoleculehaving a primary structure characterized by peptide sequences. Inaddition to the primary structure, the proteins also exhibit secondaryand tertiary structures that determine their final geometric shapes.

Because protein synthesis can be genetically directed, they can bereadily manipulated and functionalized to contain desired peptidesequences (i.e., binding sites) at desired locations within the primarystructure of the protein. The protein can then be assembled to provide atemplate.

Thus, in various embodiments, the templates are biomolecules comprisingat least one first peptide sequence and at least one second peptidesequence. In one embodiment, the templates are native proteins orproteins that can be engineered to have binding affinities fornanocrystals of at least two specific materials.

In certain embodiments, the biological templates are chaperoning, whichcan be engineered to have a binding affinity for a particular type ofnanoparticle and which can self assemble into fibrils or ordered 2-darrays (see, e.g., U.S. Patent Application 2005/0158762). Chaperoninsare a type of proteins that readily self-assemble into many differentshapes, including double-ring structures and form a crystalline array ona solid surface. Typically, adenosine triphosphate (ATP) and Mg²⁺ areneeded to mediate the crystallization. see, e.g. U.S. Patent Application2005/0158762. Examples of how digital alloys can be formed fromchaperonins are shown in FIGS. 5A, 5B, and 6.

FIGS. 5A and 5B show schematically a ring-shaped chaperonin 100 havingnine subunits 104. An open pore 108 is positioned in the center of thechaperonin. The open pore can be characterized as a functional domain,which comprises peptide sequences that can be genetically engineered tohave specific affinity for nanocrystals of specific materials. Inaddition, the functional domain has a well-defined geometry that candetermine the size of the nanocrystals nucleated thereon.

Through genetic engineering, binding sites (not shown) may be present oneach or any number of the subunits. As one example, FIG. 5A shows thatfour subunits have first binding sites that coupled to a first type ofnanocrystals 112, and five subunits having second binding sites thatcoupled to a second type of nanocrystals 116.

The subunits of the chaperonins can also be engineered to present firstbinding sites in the open pore and second binding sites on the exteriorof the chaperonin. As illustrated in FIG. 5B, chaperonin 102 is bound tonine first nanocrystals 112 in the open pore 108, and to ninenanocrystals 114 of a second type on the exterior 124.

Native chaperonins are subcellular structures composed of 14, 16 or 18identical subunits called heat shock proteins. These 60 kDa subunits arearranged as two stacked rings 16-18 nm tall by 15-17 nm wide. Manyvarieties of chaperoning have been sequenced and their structuralinformation is available to guide genetic manipulations. Mutantchaperonins, in which one or more amino acids have been altered throughsite-directed mutagenesis, can be developed to manipulate the finalshape and binding capability of the chaperoning. See, e.g., McMillan A.et al, (2002) Nature Materials, 1, 247-252. It should be understood thatgenetically engineered or chemically modified variants of chaperoningare also suitable templates as defined herein.

In another embodiment, the template is an S-layer protein, whichself-assembles into ordered two-dimensional arrays and can bind tonanocrystals. (See, e.g., Dietmar P. et al., Nanotechnology (2000) 11,100-107.) Native S-layers proteins form the outermost cell envelopecomponent of a broad spectrum of bacteria and archaea. They are composedof a single protein or glycoprotein species (Mw 40-200 kDa) have unitcell dimensions in the range of 3 to 30 nm. S-layers are generally 5 to10 nm thick and show pores of identical size (e.g., 2-8 nm). It has beendemonstrated that S-layer proteins recrystallized on solid surfaces orS-layer self-assembly products deposited on such supports may be used toinduce the formation of CdS particles or gold nanoparticles, see, e.g.,Shenton et al., Nature (1997) 389, 585-587; and Dieluweit et al.Supramolec Sci. (1998) 5, 15-19. It should be understood thatgenetically engineered or chemically modified variants of S-layerprotein are also suitable templates as described herein.

In yet another embodiment, the biological template is an apoferritin.Apoferritin is a ferritin devoid of ferrihydrite. Native ferritin isutilized in iron metabolism throughout living species. It consists of 24subunits, which create a hollow structure having a cavity of roughly 8nm in diameter surrounded by a wall of about 2 nm in thickness. Thecavity normally stores 4500 iron(III) atoms in the form of paramagneticferrihydrite. In apoferritin, this ferrihydrite is removed and othernanoparticles may be incorporated in the cavity created. The subunits ina ferritin pack tightly; however, there are channels into the cavity.Some of the channels comprise suitable binding sites that bind metalssuch as cadmium, zinc, and calcium. Ferritin molecules can be induced toassemble into an ordered arrangement in the presence of these divalentions. Detailed description of using ferritin as a template for bindingto nanocrystals can be found in, e.g., U.S. Pat. Nos. 6,815,063 and6,713,173. It should be understood that genetically engineered orchemically modified variants of apoferritin are also suitable templatesas described herein.

In a further embodiment, the template is an E. coli DNA polymerase III βsubunit, which is a homo dimeric protein. The overall structure assumesa donut shape with a cavity of about 3.5 nm and a wall of about 3.4 nmthick. The interior surface of the wall comprises twelve short a heliceswhile six β sheets form the outer surface. The interior surface can beengineered to introduce amino acid or peptide sequence that will captureor nucleate nanocrystals of various materials. It should be understoodthat genetically engineered or chemically modified variants of E. coliDNA polymerase are also suitable templates as described herein.

b. Biological Scaffolds

In other embodiments, the template is a biological scaffold to which oneor more peptide sequences are fused. “Biological scaffold” refers to acomplex multi-molecular biological structure that comprises multiplebinding sites. In preferred embodiments, the biological scaffolds aregenetically engineered to control the number, distribution, and spacingof the binding sites (e.g., peptide sequences) fused thereto.

Examples of the biological scaffolds include, without limitation, viralparticles, bacteriophages, amyloid fibers, and capsids. These biologicalscaffolds (in both their native and mutant forms) are capable of formingordered structures when deposited on a variety of solid surfaces. See,e.g., Flynn, C. E. et al., “Viruses as Vehicles for Growth, OrganizationAssembly of Materials,” Acta Materialia (2003) 51, 5867-5880; Scheibel,T. et al., PNAS (2003), 100, 4527-4532; Hartgerink, J. D. et al., PNAS(2002) 99, 5133-5138; McMillan, A. R. et al., Nature materials (2002),247-252; Douglas, T. et al., Advanced Materials (1999) 11, 679-681; andDouglas, T. et al., Adv. Mater. (2002) 14, 415-418; and Nam et al.,“Genetically Driven Assembly of Nanorings Based on the M3 Virus,”Nanoletters, a-e.

In one particular embodiment, a M13 bacteriophage can be engineered tohave one or more particular peptide sequences fused onto the coatproteins. For example, it has been demonstrated that peptide sequenceswith binding and/or nucleating affinity for gold or silver nanocrystalscan be introduced into the coat protein (see, e.g., U.S. patentapplication Ser. No. 11/254,540.)

In another embodiment, amyloid fibers can be used as the biologicalscaffold on which nanoparticles can bind and assemble into an orderednanoscale structure. “Amyloid fibers” refer to proteinaceous filament ofabout 1-25 nm diameters. Under certain conditions, one or more normallysoluble proteins (i.e., a precursor protein) may fold and assemble intoa filamentous structure and become insoluble. Amyloid fibers aretypically composed of aggregated β-strands, regardless of the structureorigin of the precursor protein. As used herein, the precursor proteinmay contain natural or unnatural amino acids. The amino acid may befurther modified with a fatty acid tail. Suitable precursor proteinsthat can convert or assemble into amyloid fibers include, for example,RADA16 (Ac−R+AD−AR+AD−AR+AD−AR+AD−A−Am) (gold-binding),biotin-R(±)GD(−)SKGGGAAAK-NH₂ (gold-binding),WSWR(+)SPTPHVVTD(−)KGGGAAAK-NH₂ (silver-binding),AVSGSSPD(−)SK(+)KGGGAAAK-NH₂ (gold-binding), and the like. See, e.g.,Stupp, S. I. et al., PNAS 99 (8) 5133-5138, 2002, and Zhang S. et al.,PNAS 102 (24) 8414-8419, 2005.

Similar to protein templates, biological scaffolds are also preferred tobe engineerable such that peptide sequences can be selectively expressedand distributed according to a certain ratio.

c. Assembling and Aggregation of the Biological Templates

The alloy formation relies on the assembling or aggregation of thetemplates, which brings the nanocrystals bound to each template intoclose proximity. In certain embodiments, the templates can assembleprior to binding to the nanocrystals. In other embodiments, thetemplates can be bound with nanocrystals prior to assembling.

Biological templates such as biomolecules and biological scaffolds havea natural tendency to aggregate in solutions or on a substrate. Somebiological templates can spontaneously self-assemble into highlycrystalline 2D or 3D structures.

FIG. 6 shows schematically an ordered 2D array 130 of templates formedby the aggregation of two types of chaperonins 134 and 138. The firsttype of chaperonins 134 is capable of binding to first nanocrystals 142within its open pore 146. The second type of chaperonins 138 is capableof binding to second nanocrystals 150 within its open pore 154. In thisembodiment, the 2D array 130 comprises 30% the first type of chaperonins134 and 70% of the second type of chaperonins 138, which correspond to30% of the first nanocrystals 142 and 70% of the second nanocrystals150. As illustrated, the relative components of the first and secondnanocrystals in a resulting alloy are determined by the ratio of theircorresponding templates.

It is noted that the templates can also be deposited or assembled toform random, polycrystalline or amorphous structures, so long as thetemplates selected comprise the desired ratio of the first and secondbinding sites, whether they are present on the same type of template orpresent on corresponding first and second type of templates.

2. Nonbiological Templates

The template may also be an inorganic template, for example, silicon,germanium, quartz, sapphire, or any other acceptable material. Thistemplate can be coupled to an appropriate ratio of binding sites thathave specific affinities for the desired components. For example,binding sites (e.g., proteins such as streptavidin or avidin) can beimmobilized at selected locations and at selected ratios to an inorganictemplate, e.g., silicon. Nanocrystals or other nanoparticles can bedirectly coupled to the binding sites. Alternatively, the nanocrystalscan be initially coupled to a binding partner of the binding sites (e.g.a biotin for streptavidin) thereby become immobilized on the siliconsubstrate through the strong affinity between the binding partners (e.g.biotin and streptavidin).

It should be understood that other binding sites, such as self-assembledsingle layers comprising functional groups, can be used to immobilizeand template nanocrystals that have a specific affinity for thefunctional group.

It is important that the binding sites (e.g., streptavidin) be patternedon the inorganic template within nanometers to tens of nanometers fromeach other to ensure that the nanocrystals bound thereto are alsoappropriately spaced. Protein immobilization and patterning on asubstrate can be achieved by any known methods in the art. For example,streptavidin can be patterned on a silicon oxide substrate in nanoscaleresolutions by nanoimprint lithography, see, e.g., Hoff, J. D. et al.,Nano Letters (4) 853, 2004.

B. Binding Sites

As discussed above, the templated formation of a digital alloy isultimately controlled by the nature, spacing and the relative ratio ofat least two types of binding sites on a template. “Binding site,” or“binding sequence,” refers to the minimal structural elements within thetemplate that are associated with or contribute to the template'sbinding activities. Preferably, the binding sites can control thecomposition, size and phase of the nanocrystals that will be coupledthereto.

As used herein, the terms “bind” and “couple” and their respectivenominal forms are used interchangeably to generally refer to ananocrystal being attracted to the binding site to form a stablecomplex. The underlying force of the attraction, also referred herein as“affinity” or “binding affinity,” can be any stabilizing interactionbetween the two entities, including adsorption and adhesion. Typically,the interaction is non-covalent in nature; however, covalent bonding isalso possible.

Typically, a binding site comprises a functional group of thebiomolecule, such as thiol (—SH), hydroxy (—OH), amino (—NH₂) andcarboxylic acid (—COOH). For example, the thiol group of a cysteineeffectively binds to a gold particle (Au). More typically, a bindingsite is a sequence of subunits of the biomolecule and more than onefunctional groups may be responsible for the affinity. Additionally,conformation, secondary structure of the sequence and localized chargedistribution can also contribute to the underlying force of theaffinity.

“Specifically binding” and “selectively binding” are terms of art thatwould be readily understood by a skilled artisan to mean, when referringto the binding capacity of a biological template, a binding reactionthat is determinative of the presence of nanocrystals of one material ina heterogeneous population of nanocrystals of other materials, whereasthe other materials are not bound in a statistically significant mannerunder the same conditions. Specificity can be determined usingappropriate positive and negative controls and by routinely optimizingconditions.

The composition of peptide sequences on a template is fixed to create aselected composition of nanoparticle building blocks, and variousdifferent peptide sequences can be arranged on the templates in a randomor an ordered way. The composition of a mixture of templates, eachdesigned with at least one peptide sequence with selective affinity ofthe material of one of the nanoparticle building blocks, can be chosento yield a given composition of nanoparticle building blocks. Thetemplates themselves may be deposited or may self-assemble in a randomor an ordered way.

An evolutionary screening process can be used to select the peptidesequence that has specific binding affinities or selective recognitionfor a particular material. Detailed description of this technique can befound in, e.g., U.S. Published Patent Application Nos. 2003/0068900,2003/0073104, 2003/0113714, 2003/0148380, and 2004/0127640, all of whichin the name of Cambrios Technologies Corporation, the assignee of thepresent application. These references, including the sequence listingsdescribed, are incorporated herein by reference in their entireties.

In brief, the technique makes use of phage display, yeast display, cellsurface display or others, which are capable of expressing wide varietyof proteins or peptide sequences. For example, in the case of phagedisplay, libraries of phages (e.g., M13 phages) can be created byinserting numerous different sequences of peptides into a population ofthe phage. In particular, the genetic sequences of the phage can bemanipulated to provide a number of copies of particular peptidesequences on the phage. For example, about 3000 copies of pVIII proteinscan be arranged in an ordered array along the length of M13 phageparticles. The pVIII proteins can be modified to include a specificpeptide sequence that can nucleate the formation of a specific targetnanocrystal. The proteins having high affinities for different, specifictarget nanocrystal can be exposed to more and more stringent environmenttill one can be selected that has the highest affinity. This protein canthen be isolated and its peptide sequence identified.

This technique is powerful because it allows for rapid identification ofpeptide sequence that can bind, with specificity, to nanocrystals of anygiven material. Moreover, as will be discussed in more detail below,once a peptide sequence is identified, it can be incorporated into abiological template in a controllable manner through geneticengineering.

The binding site can be coupled to an appropriate nanocrystal throughdirect binding or “affinity.” In this case, pre-formed nanocrystals ofpre-determined compositions and dimensions can be incubated togetherwith the templates and binding reactions take place between appropriatebinding sites and the nanocrystals.

It is also possible that the templates can cause the nanocrystals tonucleate from a solution phase on to the template. Nucleation is aprocess of forming a nanocrystal in situ by converting a precursor inthe presence of a template. Typically, the in situ generatednanocrystals bind to the template and continue to grow. As noted above,certain biological templates (e.g., proteins such as chaperonins andapoferritins) have a functional domain of controllable composition andgeometry. The functional domain therefore provides both the binding siteas well as the physical constraints such that the nucleated nanocrystalscan grow into a controllable dimension (determined by the geometry ofthe functional domain). Detailed description of forming nanoparticles bynucleation process can be found in, e.g., Flynn, C. E. et al., (2003) J.Mater. Sci., 13, 2414-2421; Lee, S—W et al., (2002) Science 296,892-895; Mao, C. B. et al., (2003) PNAS, 100, (12), 6946-6951, and U.S.Published Patent Application No. 2005/0164515.

Table 1 shows examples of peptide sequences that have been identified tohave specific affinity to a number of semiconductor and metallicmaterials. The mechanisms with which the peptide sequence interacts witha given material are also indicated.

TABLE 1 Peptide Sequence Material Type of Binding CNNPMHQNC ZnSnucleation, affinity^(1,2,3,4) LRRSSEAHNSIV ZnS nucleation,affinity^(1,3,4) CTYSRLHLC CdS nucleation, affinity¹ SLTPLTTSHLRS CdSnucleation, affinity¹ HNKHLPSTQPLA FePt nucleation, affinity^(6,7)CNAGDHANC CoPt nucleation, affinity⁶ SVSVGMKPSPRP L10 FePt: nucleation,affinity⁷ VISNHRESSRPL L10 FePt: nucleation, affinity⁷ KSLSRHDHIHHH L10FePt: nucleation, affinity⁷ VSGSSPDS Au nucleation, affinity⁸ AEEEED Ag,Co₃O₄ nucleation, affinity⁹ KTHEIHSPLLHK CoPt Affinity EPGHDAVP Co²⁺nucleation, affinity¹¹ HTHTNNDSPNQA GaAs affinity^(12,13)DVHHHGRHGAEHADI CdS nucleation, affinity¹⁴ KHKHWHW ZnS, Au, CdSaffinity¹⁵ RMRMKMK Au affinity¹⁵ PHPHTHT ZnS affinity¹⁵ CSYHRMATC Gedislocations affinity¹⁶ CTSPHTRAC Ge dislocations affinity¹⁶LKAHLPPSRLPS Au affinity⁹ ¹Flynn, C.E. et al., “Synthesis andorganization of nanoscale II-VI semiconductor materials using evolvedpeptide specificity and viral capsid assembly,” (2003) J. Mater. Sci.,13, 2414-2421. ²Lee, S-W et al., “Ordering of Quantum Dots UsingGenetically Engineered Viruses,” (2002) Science 296, 892-895. ³Mao, C.B.et al., “Viral Assembly of Oriented Quantum Dot Nanowires,” (2003) PNAS,vol. 100, no. 12, 6946-6951. ⁴US2005/0164515 ⁶Mao, C.B. et al.,“Virus-Based Toolkit for the Directed Synthesis of Magnetic andSemiconducting Nanowires,” (2004) Science, 303, 213-217. ⁷Reiss, B.D. etal., “Biological route to metal alloy ferromagnetic nanostructures”(2004) Nano Letters 4(6), 1127-1132. ⁸Huang, Y. et al., “Programmableassembly of nanoarchitectures using genetically engineered viruses”(2005) Nano Letters 5(7), 1429-1434. ⁹U.S. Patent Application No.11/254,540. ¹¹Lee, S-W. et al., “Cobalt ion mediated self-assembly ofgenetically engineered bacteriophage for biomimic Co—Pt hybrid material”Biomacromolecules (2006) 7(1), 14-17. ¹²Whaley, S.R. et al., “Selectionof peptides with semiconductor binding specificity for directednanocrystal assembly” (2000) Nature, 405(6787), 665-668.¹³US2003/0148380 ¹⁴US2006/0003387 ¹⁵Peelle, B.R. et al., “Designcriteria for engineering inorganic material-specific peptides” (2005)Langmuir 21(15), 6929-6933. ¹⁶U.S. Provisional Patent Application60/620,386.

C. Nanocrystals

“Nanocrystal”, “quantum dots”, or “nanoparticles” generally refers to ananoscale building block of the digital alloy. Nanocrystals areaggregates or clusters of a number of atoms, typically of an inorganicmaterial. As used herein, nanocrystals are typically less than 10 nm indiameter. More typically, the nanocrystals are less than 5 nm indiameter or less than 1 nm in diameter. They may be crystalline,polycrystalline or amorphous.

As described above, nanocrystals of at least two different compositions(materials) are bound to a template or place in an aggregation to forman alloy composition. In certain embodiments, a nanocrystal can be anelemental material, including metals and semiconductors. In otherembodiments, a nanocrystal can be a binary material, which is a stablecompound or alloy of two elements.

The composition of a nanocrystal thus can be represented by formulaA_(m)B_(n), wherein, A and B are single elements. The letters m and ndenote the respective atomic percentages of A and B in the nanocrystal,and are defined as 0≦m≦1; 0≦n≦1; m+n=1; provided that m and n are not 0at the same time. When n is 0, the nanocrystal is an elemental materialA. When neither m nor n is 0, the nanocrystal is a binary compoundA_(m)B_(n).

Similarly, nanocrystals of a different or second material can berepresented by formula C_(p)D_(q), in which C and D are single elementsand p and q have values 0≦p≦1; 0≦q≦1; p+q=1; provided that p and q arenot 0 at the same time.

As used herein, m and n (or p and q) are the respective atomicpercentages (atomic %) and correspond to the stoichiometric ratio of Aand B in the binary compound. They can also be in the form of properfractions. For example, a binary compound having 50% A and 50% B can berepresented by A_(0.5)B_(0.5). It should be understood that, although mand n are defined as proper fractions or atomic percentages, both ofwhich require that 0≦m≦1 and 0≦n≦1, the binary compound of A_(m)B_(n)can also be expressed in formulae containing whole numbers. One skilledin the art readily recognizes that these formulae are merely differentexpressions of the same composition. For example, A_(0.5)B_(0.5) may beexpressed as AB, A₂B₂ or A₅B₅, or any number of expressions so long asthe stoichiometric ratio of A and B (m:n) remains the same. Theseexpressions should therefore be recognized as equivalent compositions ofA_(m)B_(n).

1. Elemental Material (n=0)

Suitable metallic elements include, Ag, Au, Sn, Zn, Ru, Pt, Pd, Cu, Co,Ni, Fe, Cr, W, Mo, Ba, Sr, Ti, Bi, Ta, Zr, Mn, Pb, La, Li, Na, K, Rb,Cs, Fr, Be, Mg, Ca, Nb, Tl, Hg, Rh, Sc, Y. Suitable semiconductorelements include Si and Ge.

In certain embodiments, nanocrystals of an elemental material can bealloyed with a different elemental material to form a binary alloy. Inother embodiments, nanocrystals of an elemental material can be alloyedwith a binary compound to form a ternary alloy.

2. Binary Material (m≠0 and n≠0)

A binary material is a stable compound of two elements. In certainembodiments, the binary material or binary compound is metallic,including two metallic elements, such as Cu and Ni, Sn and In and thelike.

In other embodiments, the binary material is a semiconductor compound.Typically, when A is a Group IIIA element (e.g., Al, Ga, In or TI), B isa Group VA element (e.g., N, P, As or Sb). When A is a Group IIB element(e.g., Zn, Cd or Hg), B is a Group VIA element (O, S or Se). Many binarysemiconductors with stable compositions are known, including, withoutlimitation, AlAs, AlP, AlN, GaAs, GaP, GaN, InAs, ZnSe, CdS, InP and InNand the like.

In certain embodiments, a first binary material (A_(m)B_(n)) and asecond binary material C_(p)D_(q) are combined on a template to form aquaternary alloy, in which all four elements A, B, C and D are differentelements. In other embodiments, B and D are the same element, and thesecond binary material can be represented by C_(p)B_(q). The resultingcomposition is therefore a ternary alloy comprising A, B and C.

Metallic and semiconductor nanocrystals are commercially available from,e.g., Quantumsphere, Inc. (Santa Ana, Calif.), Invitrogen (Carlsbad,Calif.), and Nanoprobes (Yaphank, N.Y.). They can also be prepared byknown methods in the art, e.g., by sol-gel technique, pyrolysis oforganometallic precursors, and the like. These preformed nanocrystalsare prepared independently of the templates, and can be coupled to theappropriate binding sites of the template through specific affinity. Forexample, a pre-formed nanoparticle can bind directly to a binding site,typically a peptide sequence screened and identified for that particularnanoparticle. Alternatively, the nanoparticles can be surface-modifiedwith a desired binding agent, such as biotin, which can be coupled to abinding site (e.g., streptavidin) through the strong and specificaffinity between biotin and streptavidin.

In other embodiments, the nanocrystals can be nucleated from a solutionphase. Nucleation is a process of forming a nanocrystal in situ byconverting a precursor in the presence of a template. Typically, the insitu generated nanoparticle binds to and grows at least partially withinthe functional domain of the template. The precursors are typicallysoluble salts of the elements that ultimately form the nanocrystals. Forexample, nanocrystals of CdS can be nucleated out of a solutioncontaining Cd²⁺ and S²⁻. More detailed description of formingnanoparticles by nucleation process can be found in, e.g., Flynn, C. E.et al., “Synthesis and Organization of Nanoscale II-VI SemiconductorMaterials Using Evolved Peptide Specificity and Viral Capsid Assembly,”(2003) J. Mater. Sci., 13, 2414-2421; Lee, S—W et al., “Ordering ofQuantum Dots Using Genetically Engineered Viruses,” (2002) Science 296,892-895; Mao, C. B. et al., “Viral Assembly of Oriented Quantum DotNanowires,” (2003) PNAS, vol. 100, no. 12, 6946-6951, andUS2005/0164515.

D. Alloys

As discussed above, by controlling the relative amount (x:y) of thefirst binding sites and the second binding sites on a template, thefirst nanocrystals of the first material and the second nanocrystals ofthe second material can be modulated to form an alloy. In particular,where the first material is a compound represented by A_(m)B_(n), andthe second material is a compound represented by C_(p)D_(q), theresulting alloy can be represented by (A_(m)B_(n))_(x)(C_(p)D_(q))_(y),wherein,

0≦m≦1; 0≦n≦1; m+n=1; and

0≦p≦1; 0≦q≦1; and p+q=1, provided that m and n are not 0 at the sametime, and p and q are not 0 at the same time.

In certain embodiments, A, B, C and D are different from one another andthe resulting alloy is a quaternary alloy.

In other embodiments, A, B and C are different from one another, and Bis the same as D, and the resulting alloy is a ternary alloy.

In yet other embodiments, n=q=0, and the resulting alloy is a binaryalloy A_(x)C_(y), or A_(x)C_(1-x) (as x+y=1).

Alloys with versatile compositions can be achieved by selecting theappropriate nanocrystal components and by controlling the relativeamount of the corresponding binding sites on the templates.

For example, InN and GaN can be selected as the nanocrystal componentsto form an alloy of (InN)_(x)(GaN)_(y), or In_(x)Ga_(y)N_(x+y), in thepresence of templates that provide, in percentages, x binding sites thatbind specifically with InN and y binding sites that bind specificallywith GaN. Because x+y=1, the resulting alloy can also be represented byIn_(x)Ga_(1-x)N. Thus, alloys having a variety of bandgaps can beobtained by controlling the amounts of the respective binding sites. Theformations of these alloys are not restrained by lattice matching. Morespecifically, because the alloys are built from nanoscale buildingblocks (nanostructure components) on molecular level, strains anddefects typically associated with epitaxial growth are not of concern.

Other alloys that correspond to useful bandgaps include, for example,GaAs_(x)P_(1-x) (formed from GaP and GaAs), Ga_(x)In_(1-x)P (formed fromGaP and InP), Al_(x)In_(1-x)P (formed from AlP and InP) andAl_(x)Ga_(1-x)As_(y)P_(1-y) (formed from AlP and GaAs).

E. Method of Making Digital Alloys

Other embodiments describe a method of making an alloy comprising:

selecting biological templates having, in percentages, x first bindingsites and y second binding sites (0<x<1, 0<y<1), the first binding sitehaving a specific binding affinity for a first nanoparticle of a firstmaterial, the second binding site having a specific binding affinity fora second nanoparticle of a second material;

binding the first nanoparticles to respective first binding sites,

binding the second nanoparticles to respective second binding sites; and

forming the alloy comprising the first material and the second materialat a stoichiometric ratio of x:y.

In certain embodiments, the first material is a compound represented byA_(m)B_(n), the second material is a compound represented by C_(p)D_(q),the resulting alloy can be represented by(A_(m)B_(n))_(x)(C_(p)D_(q))_(y), wherein,

0≦m≦1; 0≦n≦1; m+n=1; and

0≦p≦1; 0≦q≦1; and p+q=1, provided that m and n are not 0 at the sametime, and p and q are not 0 at the same time.

In other embodiments, selecting the biological templates comprisesengineering the biological templates through genetic manipulation. Inparticular, controlling the biological template can be accomplished byengineering the biological template to express the first binding sites(e.g., first peptide sequence) and the second binding sites (e.g.,second peptide sequence) at pre-determined locations, spacings andquantities on the templates.

In a preferred embodiment, the biological template is a protein.Exemplary proteins include, without limitation, a chaperonin or agenetically engineered or chemically modified variant thereof, a S-layerprotein or a genetically engineered or chemically modified variantthereof, an apoferritin or a genetically engineered or chemicallymodified variant thereof, or an E. coli DNA polymerase III β subunit ora genetically engineered or chemically modified variant thereof.

In other embodiments, the biological template is a biological scaffoldfused with the first peptide sequence and the second peptide sequence.As discussed above, a biological scaffold can be, for example, a viralparticle, a bacteriophage, an amyloid fiber, or a capsid.

FIG. 7 illustrates a method of making a digital alloy, starting with atemplate 151 which has been engineered to have the desired ratio ofbinding sites that cause the formation of a material which emulates aternary compound of Al_(x)Ga_(1-x)As. The template 151 has a firstplurality of binding sites 152 which have an affinity for nanocrystal156, in this example AlAs. The template also contains a second pluralityof binding sites 154 which have an affinity for nanocrystal 158, in thisembodiment GaAs. The ratio of the first binding sites 152 to the secondbinding sites 154 is selected to achieve a desired composition of theresulting alloy. For example, an M13 virus can be genetically modifiedto have binding sites (e.g., peptide sequences) for these or otherselected nanocrystals at particular locations on the outer coat proteinsof the virus. The template 151 is then exposed to a fluid having aplurality of nanoparticles of the binary compound AlAs.

The AlAs nanoparticles can selectively affix themselves to therespective binding sites 152 of the template 151 and do not affix orattach to the binding sites 154. The template 151 is also exposed to afluid having GaAs nanoparticles therein and the GaAs nanoparticles affixthemselves to the binding sites 154. In some embodiments, it is desiredto have the fluids in separate liquid solutions and the template issequentially exposed to the fluids, while in other embodiments, thetemplate may be exposed simultaneously to a single liquid solutionhaving both binary components therein.

FIGS. 8 and 9 illustrate the various steps for forming a ternarycompound material according to one embodiment. In the step shown in FIG.8, any acceptable substrate, such as a template 168 is provided aspreviously illustrated and explained with respect to FIG. 7. Thetemplate 168 has a plurality of binding sites 164 and 167 thereon,having respective affinities for the desired nanocrystal component. Thenanocrystal components which are to form the digital alloy can have anydesired element composition. In the example provided for FIGS. 8-11,they are binary compositions such as InN and GaN. It is desired that thebinding sites be close enough to form a continuous material from anelectron's point of view. The spacings between adjacent binding sitesare typically on the order of nanometers and tens of nanometers. Theratio of the binding sites 164 and 167 is selected to provide thedesired number of the components of binary component 160 and binarycomponent 162. Accordingly, template 168 is engineered to containdifferent binding sites that can selectively attach to the respectivenanocrystals. In addition, the binding sites are spaced severalnanometers (e.g., less than 10 nm) apart from each other in order toprovide a continuous material

A solution is provided having a plurality of the nanocrystals 160 and162 evenly dispersed therethrough. The nanocrystals may be in the formof nanoparticles, nanorods, or any other acceptable form. In oneembodiment, a single solution is provided which has both types ofnanocrystals present. Alternatively, two separate solutions can beprovided, each of which have the nanocrystals present, evenly dispersed.A plurality of templates 168 is placed into the solution containing thenanocrystals. The solution can be mixed at room temperature and containsthe appropriate pH balances such that the template 168 is active usingtechniques well known in the art. A plurality of the templates 159 canbe deposited or self-assemble on a substrate to provide a layer of thealloy, the controllable composition of which corresponds to desiredphysical properties.

If the nanocrystals are in two separate solutions, the template 168 isplaced in a first solution and mixed until the binding sites for thatparticular nanocrystal have become attached to the appropriatenanoparticles in solution, and then the template 168 is removed from thefirst solution and placed in the second solution which contains thesecond nanocrystals 160, and the mixing continued.

When such a template is exposed to a solution having nanoparticles orquantum dots composed of material which have an affinity to therespective binding sites, then the materials will bind to the templates,which can form an ordered array of the material so that the finaltemplates 168 emulate a ternary alloy having three different elements inrespective ratios rather than two different binary compounds. The use ofnanocrystals, quantum dots, and nanoparticles permit the templatedformation of such nanoscale materials which will emulate for physical,chemical, and electric purposes a ternary alloy.

The template 168 can be constructed to build many different alloys ofdifferent compositions. For example, the pVIII protein can be engineeredwith particular peptide sequences for use as a template. The peptidesequences to provide selective affinity and linking to varioussemiconductor nanocrystals, such as ZnS or CdS, are known or can bescreened and identified by known methods. For example, an A7 and a Z8peptide on a pVIII protein are known to recognize and control the growthof ZnS while a J140 provides selective recognition of CdS. See “Viralassembly of oriented quantum dot nanowires” by Mao et al. PNAS, Jun. 10,2003, Vol. 100, No. 12 and “Synthesis and organization of nanoscaleII-VI semiconductor materials using evolved peptide specificity andviral capsid assembly” by Flynn et al. J. Mater. Chem., 2003, Vol. 13,pages 2414-2421, each of which are incorporated herein by reference.

Other templates using different peptide combinations can be used tocreate substrates for forming compositions having In, Ga, Al, As, N, P,and various other elements in binary compositions to emulate a ternaryor quaternary compound.

One strength of the technique is that the very same binary componentscan be used to create different ternary compounds having differentbandgaps using the same nanoparticles, as illustrated in FIGS. 10 and11. As illustrated in FIG. 10, a template 161 is provided having a firstselected ratio of binding sites 167 to binding sites 164. In the exampleshown, there are eight binding sites 167 for every two binding sites164. When the template 161 is exposed to a liquid solution having aplurality of nanoparticles of InN 160 and GaN 162, the respectivenanoparticles bind to the binding sites for which they have a specificaffinity, thus creating a final composition of In_(0.2)Ga_(0.8)N.

FIG. 11 illustrates a different template 163 in which the same bindingsites 164 and 167 are engineered to have a different ratio with respectto each other. In this example, the binding sites 164 have a ratio tothe binding sites 167 of 3:7 or 30%:70%. Accordingly, when the template163 is exposed to the same liquid solution having the binarynanoparticles, a different ratio of the nanocrystals affixes to thetemplate. In the event the nanoparticles are InN and GaN, a finalcomposition will be formed having the properties of In_(0.3)Ga_(0.7)N.Any desired ratio of the nanocrystal components can be formed in thepresence of templates, which in turn controls the final alloycomposition, such as In_(0.35)Ga_(0.65)N, etc.

F. Applications

Alloys compositions described herein correspond to useful opto-,electrical and mechanical properties that may not be attainable throughconventional means of multi-component alloying or compounding. Driven bythe powerful techniques of genetically engineering a given biologicaltemplate, alloys of highly customizable compositions can be obtained bycontrolling the different binding sites on the templates that correspondto respective nanocrystals components.

Thus, various embodiments are directed to devices that utilize alloycompositions described herein.

1. Photovoltaic Cells or Solar Cells

Solar radiation provides a usable energy in the photon range ofapproximately 0.4 eV to 4 eV. Optoelectronic devices such asphotovoltaic cells can harvest and convert certain photon energies inthis range to electrical power. Typically, the optoelectrical device isbased on a semiconductor material with a direct bandgap that matches agiven photon energy. With the absorption of the photon energy, electronsin the valence band can be excited to the conduction band, where theelectrons are free to migrate. Similarly, holes are generated in thevalence band. The migration of these charge carriers (e.g., electronsand holes) forms an electrical current.

The bandgaps of currently available semiconductor materials onlycorrespond to a narrow portion within the broad range of the solarradiation. Light with energy below the bandgap of the semiconductor willnot be absorbed or converted to electrical power. Light with energyabove the bandgap will be absorbed, but electron-hole pairs that arecreated quickly recombine and lose the energy above the bandgap in theform of heat. For example, photovoltaic cells based on crystallinesilicon have a direct bandgap of about 1.1 eV, lower than most of thephoton energies. Silicon-based solar cells therefore have about 25%efficiency at best.

Thus, existing photovoltaic cells have intrinsic efficiency limitsimposed by the semiconductor materials. Currently, no one semiconductormaterial has been found that can completely match the broad ranges ofsolar radiation.

Higher efficiencies have been sought by using stacks of semiconductorswith different bandgaps, which provide solar cells having one or morejunctions. Stacks formed from two semiconductors, Ga_(0.5)In_(0.5)P/GaAsand three semiconductors Ga_(0.5)In_(0.5)P/GaAs/Ge have been developedover the last decade. These multi-junction cells take advantages of therelatively good lattice match of Ga_(0.5)In_(0.5)P, GaAs and Ge.Typically, in a multi-junction cell with layers of differentcompositions, lattice matching is critical in producing low-defect ordefect-free crystals. Crystal defects negatively impact the opticalproperties of the semiconductor because the defects trap charge carriersand limit the current and voltage obtainable. Accordingly,multi-junction cells are typically limited by a general lack ofappropriate semiconductor materials that can be integrated at low cost.

It was recently realized that the ternary alloys (In_(x)Ga_(1-x)N) couldbe used as the basis of a full-spectrum solar cell, see, U.S. PublishedPatent Application 2004/0118451, but many technical challenges remain ingrowing well-controlled, epitaxial layers of In_(x)Ga_(1-x)N.

The semiconductor alloys described herein provide tunable bandgapsthrough compositional control in the presence of templates, without theconcerns of lattice and polarity match. It is possible to create alloycompositions with bandgaps that correspond to the entire range of thesolar radiation.

FIGS. 12A and 12B illustrate solar cells 174 composed using an array ofdigital alloys according to principles of the present invention. Thesolar cell 174 is composed of a semiconductor material having threelayers of a customized digital composition made as described herein. Thesolar cell 174 has electrodes 182 on a side region thereof. In oneembodiment, a low resistance electrical layer composed of a highly dopedsemiconductor or some other contact material is coupled to an electrodein the top region thereof. It is also known in the art to use a GaAssubstrate as a base material to which a conducting electrode is affixedin order to complete the electrical circuit for the generation ofelectricity from the solar cell, and such structures fall within the useof this invention, even though not shown in the figures. A GaAs layer byitself is known to produce electricity when exposed to sunlight atefficiencies in the range of 16%-25% with efficiencies of 20%-25% beingachieved. This efficiency can be substantially improved using structuresas disclosed herein.

As shown in FIG. 12A, a solar cell is formed that is composed of aplurality of digital alloys constructed using the methods disclosedherein, as previously illustrated with respect to FIGS. 7-11. A layer orlarge array of digital alloys templates constructed based on theprincipals of FIGS. 7-11 are formed into three separate layers 176, 178,and 180. The ratio of the nanocomponents in the layer 176 is selected toemulate a ternary compound having the properties of In_(x3)Ga_(y3)N.This material will have the desired bandgap and electrical propertieswhen exposed to sunlight to produce electricity from differentfrequencies of sunlight than that which are produced by the layers 178and 180. Accordingly, the layer 176 will be extracting energy fromdifferent portions of the light frequency than is being extracted bylayers 178 and 180, thus resulting in greater overall efficiencies ofthe solar cell 174.

Similarly, layers 178 and 180 are formed adjacent to and on top of thelayer 176 into a single structure. These layers are also composed of aplurality of binary nanocrystals of the very same binary compounds ofInN and GaN, but different ratios. The respective ratios of thecompounds are varied in order to emulate a quaternary compound havingthe optoelectrical properties to extract energy from different parts ofthe sunlight spectrum. Since the same binary materials are used, it ispossible in some structures that the crystalline lattice structure willbe compatible and the adjacent layers 178 and 180 can be formed in thesame crystalline structure and in physical contact with each other. Thethree, four, or five layers of semiconductors, each having a slightlydifferent ratio of elements, provides a very efficient solar cell.

As shown in FIGS. 12A-12B, a solar cell 174 can, of course, be composedof a wide variety of different digital alloy materials using anycombination of the nanocrystals or nanoparticles disclosed in theapplication. For example, the digital alloys for any one of layers 176,178, and 180 may include compounds that include additional elements suchas P, Al, Cd, cadmium-selenide, cadmium-telluride and other materials.One advantage of the present invention is that the different componentsneed not have similar lattice constants and may not alloy or chemicallybind to each other under standard conditions. For example, GaP may beformed in the same digital alloy with InSb or InAs using binding sitesadjacent to each other along a template according to principlesdiscussed herein. Since these materials have vastly different latticeconstants, forming them in the same substrate in a conventional cellwould be difficult or impossible. However, the templated formation ofnanocrystals which bind to a template in selected ratios based on theaffinity to the binding sites rather than based on lattice matching orother constraints permits material having different lattice constantsand different properties to be combined into a digital alloy.Accordingly, in one embodiment the digital alloy of the solar cell ofFIG. 12A may include materials whose lattice constants are spacedgreater than 0.3 Å to 0.5 Å apart from each other (see the chart in FIG.1), or in some instances greater than 1 Å apart from each other and yetstill be provided in the same layer of a digital alloy in thesemiconductor material formed using templates according to the presentinvention.

FIG. 12B illustrates a different construction of a solar cell accordingto another embodiment. In this construction, electrodes 182 are on thetop and bottom of the cell 174 of electrodes 184 are in betweenrespective layers 186, 187, and 188. In the solar cell of FIG. 12B, thetop layer 186 may be a standard binary material, such as GaN under whichare two or more layers 187 and 188 having different bandgap propertiesthan the uppermost layer 186. The operation of the various layers inFIGS. 12A and 12B is illustrated in FIG. 13.

A solar cell represented schematically as 174 has sunlight impingedthereon, as shown in FIG. 13. The sunlight has multiple frequenciesacross a wide spectrum. The topmost material 180 has a first bandgapE_(G1) and produces electricity at a first efficiency based on thefrequency to which it is tuned for the sunlight. The second material 178has a specifically tuned bandgap E_(G2) in order to extract energy froma different frequency spectrum than the material 180. This bandgapE_(G2) is therefore effective to generate additional electricity,greatly boosting the overall efficiency of the solar cell 174.Subsequent layers, one or more, represented as 176 have a differentbandgap, in this embodiment less than the bandgaps of the layers 180 and178, and generate electricity based on different parts of the spectrum,further boosting the overall efficiency of the solar cell 174.Electricity can be generated to a load 190 shown in FIG. 12B, andsimilar circuits can be placed on the solar cell of FIG. 12A beingattached to electrodes 182, the load not being shown for simplicity.

FIG. 14 illustrates nanocrystals in the form of a plurality of nanorodswhich may be used according to principles disclosed herein. A substrate192 can be provided as a template using the techniques explained herein.The nanocrystals are formed from various nanorods, each having differentoptoelectrical properties. A first plurality of nanorods 194 has a firstbandgap. A second plurality of nanorods 196 has a second bandgap, whilea third plurality of nanorods 198 have a third bandgap. Specific bindingsites for each of these nanocrystals are provided on the template 192.The template 192 therefore has, on the single template, a large varietyof nanorods each having different optoelectrical properties adjacent toeach other. One of the uses of such a composition is shown in FIG. 15 inwhich the template 192 is impregnated within a conductive material so asto act as an electrode in a solar cell. A top electrode 191 may also beprovided. Sunlight impinging upon the composition 151 will generateelectricity separately from each of the different nanorods 194, 196, and198. Each of these nanorods are custom engineered to have a differentbandgap and thus generate electricity from different portions of thesunlight spectrum.

Accordingly, a single layer of material can be formed to provide veryefficient solar cells. This layer of material can be incredibly thin,since the nanorods are in the nanocrystal range. In some embodiments,the nanocrystals which form the nanorods 194, 196, and 198, have widthsin the range of 6-10 nanometers and lengths in the range of 500-800nanometers. Such dimensions correspond to those of templates based onbiological viruses, such as the M13 or phages which have been discussedherein and disclosed in the articles which are incorporated byreference. Accordingly, a solar cell 199 can be provided having a totalthickness of less than 1,000 nanometers which is capable of producingelectricity from sunlight using all of the frequencies available in thesunlight spectrum. If it is desired to further improve the efficiency,additional types of nanocrystals, in the form of nanorods havingdifferent bandgaps, can be provided parallel to those shown in FIGS. 14and 15, each group of the nanorods absorbing sunlight from differentfrequencies of the spectrum and producing electricity based on thatabsorbed. A further advantage of the structure of FIGS. 14 and 15 isthat all of the sunlight impinges equally on each of the nanorodswithout having to pass through various layers before reaching abottom-most layer. Accordingly, even greater efficiencies for theproduction of electricity can be obtained using the structures of FIGS.14 and 15.

2. Lithium Ion Batteries

A further use of the digital alloys according to the present inventionis in lithium ion batteries, shown in FIGS. 16-18. A lithium battery hasan anode and a cathode, the cathode usually including carbon in variousgraphite forms having lithium atoms intercalated therein and an anodewhich generally includes Co, Mn, O or some other metal oxide. It wouldbe advantageous to have lithium ion batteries with substantially lowerresistance and higher production capability over a longer life. One ofthe difficulties is that the materials currently used have limitedconductivity and the properties which are conducive to use as an anodeor cathode in a lithium ion battery are not conducive to low-resistancetransfer of current.

According to the embodiments disclosed herein, a digital alloy can beformed having a highly conductive metal added to the cathode, oralternatively the anode or both, in a lithium ion battery to drasticallyincrease the conductivity, the current production, and the operatinglifetime of the lithium ion battery.

Gold (Au) is a highly conductive metal. If too many Au atoms ornanocrystals of Au are provided in the cathode or anode, the lithium ionbattery operation will be impaired. Using currently known constructionand alloy techniques, it is very difficult to add just a few atoms of ametal, such as Au, and have it be properly spaced and at the correctratio so as to increase the conductivity without interfering with theelectrical production capabilities of the battery. For example, it isknown to produce a molecule of AuCo. However, if all of the Co in thebattery is bound up to a corresponding Au atom, the operation of thelithium ion battery is substantially impaired.

According to principles taught herein, a selected ratio of Au to Co canbe provided which will substantially increase the conductivity andcurrent production capabilities of the battery without impairing theoperational characteristics of the lithium battery. FIG. 16 illustratesa template 202 having a selected ratio of binding sites for nanocrystalsof Au and nanocrystals of Co. The ratios are selected to have very fewnanocrystals of Au so as to provide increased conductivity withoutinterfering with the operation of the battery.

FIGS. 16 and 17 illustrate two different templates 202 which may be usedas a substrate having an affinity for different nanocrystals of singleelements. In the example of FIGS. 16-18, the substrate 202 is formedhaving a protein having an affinity for Co at regions 206 and a proteinhaving an affinity for Au at regions 204. The regions 206 and 204 arelinked to each other to form a continuous template 202. The ratio of theregions 206 and 204 are selected to specifically obtain a desired alloyin the final composition. Whereas, it may be difficult to provide acompound or alloy having a specific ratio of Co to Au in themetallurgical arts, using the template 202 having different proteinswhich attract and have an affinity for nanoparticles of the particularelements is able to achieve the construction of an AuCo havingengineered ratios of a specific desired amount. In the example of FIG.16, the ratio is approximately 6:1 of Co to Au whereas a different ratiois easily obtainable using different lengths for the proteins, as shownin FIG. 17.

FIG. 18 illustrates a lithium ion battery having a reduced resistivityof the electrode by the introduction of highly conductive gold atoms atparticular locations in the membrane. These gold atoms are attached intothe membrane using engineered proteins as has previously been described.

In the example of FIGS. 16 and 17, the template 202 binds tonanocrystals made of a single element. The single element can be a metalsuch as Au, Ag, Co, Li, C, or any one of the many semiconductors.Templates can also be constructed which have binding sites forindividual elements at some locations and for binary compounds at otherlocations so as to provide selected ratios of ternary compounds whichcould not be obtained using standard alloy and/or molecule combinationmethods.

3. LED

Another embodiment of this invention would involve improved colorcontrol for light emitting diodes.

FIG. 19 illustrates an LED 220 constructed according to embodimentsdisclosed herein. The LED includes an anode at a first semiconductorregion 224 and a cathode at a second semiconductor region 226 having ajunction 232 therebetween. Respective electrodes 22 are coupled to theends of the diodes which are connected by wires 228 and 230 to a powersource Vs. When power is supplied across the depletion region 232 at thejunction 232, light is emitted from the diode according to principleswell known for light-emitting diodes.

According to principles discussed herein, the color of the light can bespecifically engineered to be a desired wavelength. This can be done byselecting the nanocrystals which will be present in the anode 224 andcathode 226 and the respective ratios thereof.

Currently, different colors are achieved by making changes in thesemiconductor composition of the chip.http://www.olympusmicro.com/primer/lightandcolor/ledsintro.html. Forexample, “[d]epending on the alloy composition, III-nitride devicesachieve band gaps ranging from 1.9 eV indium nitride to 3.4 eV galliumnitride (GaN) to 6.2 eV aluminum nitride. The emission wavelengths . . .vary from violet to green (390 to 520 nm) as a function of the indiumcontent in the InGaN active layers.”http://oemagazine.com/fromTheMagazine/ju101/ondisplay.html “Color of thelight depends on the chemical composition of the semiconductor chip

Smaller atoms leading to higher energy light of shorter wavelength oftenhave zinc blend or wurtzite crystal structure, derived from the diamondstructure. Some common compositions: GaAs_(x)P_(1-x) Ga_(x)In_(1-x)PAl_(x)In_(1-x)P Al_(x)Ga_(y)In_(z)P Ga_(x)In_(1-x)N. Atoms withsubscripts can substitute for one another in the original structureallowing the color of the emitted light to be tuned”.http://mrsec.wisc.edu/Edetc/IPSE/educators/leds.html.

It is very difficult to achieve precise control of the semiconductorcomposition in vapor deposition, thus necessitating the use of expensivebinning and inventory techniques by LED manufacturers. “LEDs have a widespread in intensity and color. This is true even for one singleproduction batch. Therefore, binning is a must.”http://www.chml.com/led_laboratory.php.

By judicious choice of templates, LEDs manufactured with digital alloyscan have a tighter color distribution. It is possible to controlprecisely the composition of a mixture of templates since they can bemixed accurately in solution. It is also possible to fix the digitalalloy composition precisely by designing the templates to comprise thedesired ratio of appropriate peptide sequences which eliminates the needfor mixing two or more different types of templates together. Further,the digital alloy is made at room temperature in solutions held in glasscontainers, greatly reducing the cost.

Examples of various LED applications can be found at:

http://mrsec.wisc.edu/Edetc/IPSE/educators/leds.html

http://www.ieee.li/pdf/viewgraphs_lighting.pdf

http://spiedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG005941000001594112000001 &idtype=cvips&gifs=yes

http://www.lum ileds.com/pdfs/techpaperspres/presentation_SAE %202004_kern.PDF

http://www.transporteon.com/Superlatives-L/LED.php

http://www.everlight.com/en_NewsDetail.asp?newsID=200407001

http://www.nichia.com/product/phosphors.html andhttp://www.mt-berlin.com/frames_cryst/descriptions/led_phosphors.htm

http://www.electrochem.org/publications/jes/samples/JES-H47_(—)1.pdf

4. Intermetallic Layer

In addition to tailoring electronic and optical properties, it can alsobe advantageous to use digital alloys to improve the mechanicalperformance of materials. As an example, the composition ofinterconnection materials plays a significant role in the mechanicalstrength of the interconnect. When the composition at the interconnectinterface is optimized, particular intermetallic morphologies are formedwhich improve the bond strength of the interconnect and which can alsoimprove the diffusion characteristics for better long-term stability.Conversely, if the composition at the interface is not well controlled,a brittle intermetallic phase can form which will lead to aninterconnection with low bonding strength. (See, e.g., Wu, et al, J.Elect. Matls., Vol. 34, No. 11, p. 1385; Lee and Subramanian, J. Elect.Matls., Vol. 34, No. 11, p. 1399; Tai, et al, J. Elect. Matls., Vol. 34,No. 11, p. 1357)

FIG. 20 shows an intermetallic layer 250 forming an interface between afirst conductive layer 254 and a second conductive layer 258. In oneembodiment, the intermetallic layer is based on a digital alloy, asdescribed herein. The formation of such an intermetallic layer allowsfor a precision control of the composition and location of a mixture ofmetal nanoparticles at the interface, which provides a method ofcontrolling the metallic composition and morphology of the interconnectfor improved interconnection properties.

Since nanoparticles have lower melting temperatures than thecorresponding bulk material, intermetallic formation can occur at lowerprocessing temperatures. The incorporation of nanoparticles with theappropriate composition that are localized appropriately within themicrostructure of the interconnection can also improve the long-termstability of the interconnect bond through stress relief and preventionof dislocations at the grain boundaries.

As a particular example, an Auln intermetallic layer at the solder/padinterface acts as a diffusion barrier and prohibited the formation of abrittle Au intermetallic phase. (See, e.g. Wu, et al, J. Elect. Matls.,Vol. 34, No. 11, p. 1385; Lee and Subramanian, J. Elect. Matls., Vol.34, No. 11, p. 1399; and Tai, et al, J. Elect. Matls., Vol. 34, No. 11,p. 1357.) The cost of In prevents its widespread use as a majorcomponent in lead-free solder. According to the method described herein,it is possible to localize a higher In concentration at the interface toform the intermetallic interfacial layer. The morphology of theintermetallic has a direct impact on bonding strength, and the formationof column-shaped (Cu_(0.74)Ni_(0.26))₆ (Sn_(0.92)In_(0.08))₅intermetallic compounds leads to better bond strengths. These compoundswere conventionally formed by, for example, annealing for 500 h at 150°C. According to the method described herein, the intermetallic compoundcould be advantageously formed directly from nanoparticles ofCu_(0.74)Ni_(0.26) and Sn_(0.92)In_(0.08) that are localizedappropriately with a template, especially since the bond strength goesdown under lower temperature aging conditions when a differentintermetallic morphology is formed.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A composition comprising: a plurality of templates, each templatecomprising at least one first binding site and at least one secondbinding site, the first binding site having a specific binding affinityfor a first nanoparticle of a first material, the second binding sitehaving a specific binding affinity for a second nanoparticle of a secondmaterial, wherein the templates are selected to include, in percentages,x first binding sites and y second binding sites; a plurality of thefirst nanoparticles bound to respective first binding sites; a pluralityof the second nanoparticles bound to respective second binding sites;wherein the templates are assembled such that the first material and thesecond material form an alloy at a stoichiometric ratio of x:y.
 2. Thecomposition of claim 1 wherein the first material is a compoundrepresented by A_(m)B_(n), the second material is a compound representedby C_(p)D_(q) and the alloy can be represented by(A_(m)B_(n))_(x)(C_(p)D_(q))_(y), wherein, A, B, C and D are elements ofthe Periodic Table; 0≦m≦1; 0≦n≦1; m+n=1; and 0≦p≦1; 0≦q≦1; and p+q=1,provided that m and n are not 0 at the same time, and p and q are not 0at the same time.
 3. The composition of claim 2 wherein A, B, C, D aredifferent elements, and the alloy is a quaternary alloy.
 4. Thecomposition of claim 2 wherein A, B and C are different element, D isthe same as B, and the alloy is a ternary alloy.
 5. The composition ofclaim 2 wherein n=q=0, and the alloy is a binary alloy.
 6. Thecomposition of claim 2 wherein A, B, C and D are semiconductor elements.7. The composition of claim 6 wherein A and C are each independently aGroup IIIA element, and B and D are each independently a Group VAelement.
 8. The composition of claim 7 wherein the alloys isGa_(x)In_(1-x)As_(y)P_(1-y).
 9. The composition of claim 7 wherein thealloy is Ga_(x)In_(1-x)N, Ga_(x)In_(1-x)P or Al_(x)In_(1-x)P.
 10. Thecomposition of claim 2 wherein A and C are each a Group IIB element, Band D are each a Group VIA element.
 11. The composition of claim 2wherein A, B, C and D are each independently a metallic element.
 12. Thecomposition of claim 1 wherein the template is a biological template.13. The composition of claim 12 wherein the first binding site is afirst peptide sequence, and the second binding site is a second peptidesequence.
 14. The composition of claim 13 wherein the template isengineered such that the first binding sites and the second bindingsites are distributed on the template at controllable number anddistance from each other.
 15. The composition of claim 12 wherein thetemplate is a protein, and the first peptide sequence and the secondpeptide sequence are portions of the primary structure of the protein.16. The composition of claim 15 wherein the protein is a chaperonin or agenetically engineered or chemically modified variant thereof, a S-layerprotein or a genetically engineered or chemically modified variantthereof, or an apoferritin or a genetically engineered or chemicallymodified variant thereof.
 17. The composition of claim 13 wherein thetemplate is a biological scaffold fused with the first peptide sequenceand the second peptide sequence.
 18. The composition of claim 17 whereinthe biological scaffold is a viral particle, a bacteriophage, an amyloidfiber or a capsid.
 19. The composition of claim 1 wherein the templatescomprise a first type of templates and a second type of templates, thefirst type of templates having only the first binding sites, and thesecond type of templates having only the second binding sites.
 20. Amethod of forming an alloy comprising; forming at least one biologicaltemplate having at least one first binding site and at least one secondbinding site, the first binding site having a specific binding affinityfor a first nanoparticle of a first material, the second binding sitehaving a specific binding affinity for a second nanoparticle of a secondmaterial; controlling the template such that the first binding sites andthe second binding sites have a number ratio of x:y (0≦x≦1, 0≦y≦1);binding the first nanoparticles to respective first binding sites;binding the second nanoparticles to respective second binding sites; andforming the alloy comprising the first material and the second material.21. The method of claim 20 wherein the first binding site is a firstpeptide sequence, and the second binding site is a second peptidesequence.
 22. The method of claim 20 wherein controlling the biologicaltemplate comprising engineering the biological template to express thefirst peptide sequence and the second peptide sequence at pre-determinedlocations and at pre-determined quantities.
 23. The method of claim 22wherein the biological template is a protein.
 24. The method of claim 23wherein the protein is a chaperonin or a genetically engineered orchemically modified variant thereof, a S-layer protein or a geneticallyengineered or chemically modified variant thereof, or an apoferritin ora genetically engineered or chemically modified variant thereof.
 25. Themethod of claim 23 wherein the biological template is a biologicalscaffold fused with the first peptide sequence and the second peptidesequence.
 26. The method of claim 25 wherein the biological scaffold isa viral particle, a bacteriophage, an amyloid fiber, or a capsid. 27.The method of claim 20 wherein the first material is a compoundrepresented by A_(m)B_(n), the second material is a compound representedby C_(p)D_(q) and the alloy can be represented by(A_(m)B_(n))_(y)(C_(p)D_(q))_(x), wherein, A, B, C and D are elements ofthe Periodic Table; 0≦m≦1; 0≦n≦1; m+n=1; and 0≦p≦1; 0≦q≦1; and p+q=1,provided that m and n are not 0 at the same time, and p and q are not 0at the same time.
 28. The composition of claim 27 wherein A and C areeach independently a Group IIIA element, and B and D are eachindependently a Group VA element.
 29. The composition of claim 27wherein A and C are each independently a Group IIA element, and B and Dare each independently a Group VIA element.
 30. The composition of claim27 wherein A, B, C, D are different elements, and the alloy is aquaternary alloy.
 31. The composition of claim 27 wherein A, B and C aredifferent element, D is the same as B, and the alloy is a ternary alloy.32. The composition of claim 27 wherein n=q=0, and the alloy is a binaryalloy.
 33. An optoelectronic device comprising an alloy, the alloyincluding: a plurality of templates, each templates having a firstplurality of binding sites and a second plurality of binding sites, thetemplate having a selected ratio of the first binding sites to thesecond binding sites; a plurality of first nanoparticle componentscoupled to the first plurality of binding sites on the biologicaltemplate, the first component being composed of at least two differentelements; a plurality of second nanoparticle components being coupled tothe second plurality of binding sites on the template, the secondcomponent being composed of at least two different elements, at leastone element of the second component being different from at least oneelement of the first component; the ratio of the number of first bindingsites to the second binding sites being selected so that the templatescan assemble the first plurality of nanoparticles and the secondplurality of nanoparticles into the alloy.
 34. The optoelectronic deviceaccording to claim 33 wherein the first nanoparticle is a compoundrepresented by A_(m)B_(n), the second material is a compound representedby C_(p)D_(q) and the alloy can be represented by(A_(m)B_(n))_(y)(C_(p)D_(q))_(x), wherein, A, B, C and D are elements ofthe Periodic Table 0≦m≦1; 0≦n≦1; m+n=1; and 0≦p≦1; 0≦q≦1; and p+q=1,provided that m and n are not 0 at the same time, and p and q are not 0at the same time.
 35. The optoelectronic device of claim 34 wherein A,B, C, D are different elements, and the alloy is a quaternary alloy. 36.The optoelectronic device of claim 34 wherein A, B and C are differentelement, D is the same as B, and the alloy is a ternary alloy.
 37. Theoptoelectronic device according to claim 36 wherein A is Indium, B isNitrogen, and C is Gallium.
 38. The optoelectronic device according toclaim 37 wherein the ratio of the first binding sites to the secondbinding sites is selected such that alloy has the composition ofIn_(x)Ga_(1-x)N, x:(1-x), x being the atomic percentage of InN in thealloy.
 39. The optoelectronic device of claim 34 wherein n=q=0, and thealloy is a binary alloy.
 40. The optoelectronic device of claim 33wherein a spacing between adjacent binding sites is less than 10 nm. 41.The optoelectronic device according to claim 40 wherein the ratio offirst binding sites to the second binding sites is controlled bygenetically engineering the template.
 42. The optoelectrical deviceaccording to claim 33, wherein the alloy forms a first semiconductormaterial layer and a second semiconductor material layer, and theoptoelectrical device further comprises: a first electrode coupled tothe first semiconductor material layer; a second electrode coupled tothe second semiconductor material layer, and a source of electric powercoupled to the first electrode and to the second electrode to provide alight-emitting diode.
 43. A solar cell structure comprising: asemiconductor substrate; a light sensitive layer coupled to thesemiconductor substrate, the light sensitive layer comprising an alloy,wherein the alloy includes: a plurality of templates, each templateshaving a first plurality of binding sites and a second plurality ofbinding sites, the template having a selected ratio of the first bindingsites to the second binding sites; a plurality of first nanoparticlecomponents coupled to the first plurality of binding sites on thebiological template, the first component being composed of at least twodifferent elements; and a plurality of second nanoparticle componentsbeing coupled to the second plurality of binding sites on the template,the second component being composed of at least two different elements,at least element of the second component being different from at leastone element of the first component, the ratio of the number of firstbinding sites to the second binding sites being selected so that thetemplates can assemble the first plurality of nanoparticles and thesecond plurality of nanoparticles into the alloy.
 44. The solar cellstructure according to claim 43 wherein the first nanoparticle is acompound represented by A_(m)B_(n), the second material is a compoundrepresented by C_(p)D_(q) and the alloy can be represented by(A_(m)B_(n))_(y)(C_(p)D_(q))_(x), wherein, A, B, C and D are elements ofthe Periodic Table; 0≦m≦1; 0≦n≦1; m+n=1; and 0≦p≦1; 0≦q≦1; and p+q=1,provided that m and n are not 0 at the same time, and p and q are not 0at the same time.
 45. The solar cell structure according to claim 44wherein A and C are each selected from group III or II of the periodicchart and B=D and is selected from group V or VI, respectively of theperiodic chart.
 46. The solar cell structure according to claim 45wherein A and C are each selected from group III of the periodic chartand B is selected from group IV of the periodic chart.
 47. The solarcell structure according to claim 45 wherein A is Gallium, B is Indiumand C is Nitrogen.
 48. The solar cell structure according to claim 45wherein A is Aluminum, B is Gallium and C is Arsenic.
 49. The solar cellstructure according to claim 44 wherein A is Indium, B is Phosphorous, Cis Aluminum and D is Nitrogen.
 50. The structure according to claim 44wherein A is Aluminum, B is Arsenic, C is Gallium and D is Indium. 51.The structure of claim 44, further including: a second light sensitivelayer coupled to the light sensitive layer, the second light sensitivelayer comprising a second alloy, the second alloy being represented by(A′_(m′),B′_(n′))_(y′)(C′_(p′),D′_(q′))_(x′), wherein, A′, B′, C′ and D′are elements of the Periodic Table; 0≦m′≦1; 0≦n′≦1; m′+n′=1; and 0≦p′≦1;0≦q′≦1; and p′+q′=1, provided that m and n are not 0 at the same time,and p and q are not 0 at the same time, and provided that at least oneof A′, B′, C′, D′, x′, y′ m′, n′, p′ and q′ is different from,respectively, A, B, C, D, x, y, m, n, p and q.
 52. A lithium-ion batterycomprising: an anode that includes cobalt, oxygen and a low resistivitymetal selected from the group consisting essentially of gold, copper andsilver, the ratio of the low resistivity metal to the cobalt beingselectively controlled to be less than 4 and positioned within the anodeto reduce the cell resistance of the battery; a cathode; and anelectrolyte fluid positioned between the anode and the cathode totransfer lithium ions, wherein, the cobalt and low resistivity metalsare formed in the present of a plurality of templates, each templatehaving a plurality of first binding sites with an affinity for cobaltand a plurality of second binding sites with an affinity for the lowresistivity metal, the number of the binding sites for the lowresistivity metal being substantially less than the number of thebinding sites for the cobalt and having a selected ratio of first andsecond binding sites.
 53. The lithium-ion battery of claim 52 whereinthe template is a biological template that can be genetically engineeredto control the locations and quantities of the first and second bindingsites.
 54. The lithium-ion battery of claim 52 wherein a higherconcentration of the low resistivity metal is located adjacent toelectrode connection than is located in regions of the anode closest toan outside terminal.
 55. The lithium-ion battery of claim 52 furtherincluding: an cathode that includes carbon and a low resistivity metalselected from the group consisting essentially of gold, copper andsilver, the ratio of the low resistivity metal to the carbon beingselectively controlled to be less than 1 and positioned within the anodeto reduce the cell resistance of the battery.
 56. A structurecomprising: a first conductive layer; a second conductive layer; and anintermetallic layer positioned between the first conductive layer andthe second conductive layer, the intermetallic layer being formed byforming at least one biological template having at least one firstbinding site and at least one second binding site, the first bindingsite having a specific binding affinity for a first nanoparticle of afirst material, the second binding site having a specific bindingaffinity for a second nanoparticle of a second material, controlling thetemplate such that the first binding sites and the second binding siteshave a number ratio of x:y (0<x<1, 0<y<1), binding the firstnanoparticles to respective first binding sites, binding the secondnanoparticles to respective second binding sites; and forming an alloycomprising the first material and the second material.
 57. The structureof claim 56 wherein the first material is a compound represented byA_(m)B_(n), the second material is a compound represented by C_(p)D_(q)and the alloy can be represented by (A_(m)B_(n))_(y)(C_(p)D_(q))_(x),wherein, A, B, C and D are elements of the Periodic Table; 0≦m≦1; 0≦n≦1;m+n=1; and 0≦p≦1; 0≦q≦1; and p+q=1, provided that m and n are not 0 atthe same time, and p and q are not 0 at the same time.
 58. The structureof claim 57 wherein A, B, C and D are each independently a metal.